Fuel injection method for an internal combustion engine

ABSTRACT

A fuel injecting method and a corresponding arrangement for an internal combustion ( 10 ), especially of a motor vehicle, wherein a first injection takes place during an induction stroke. Proceeding from operating characteristic variables of the engine ( 10 ), a tendency-to-knock signal is determined which characterizes the tendency to knock of the engine ( 10 ). At least one second injection takes place when the tendency-to-knock signal exceeds a threshold value. (FIG.  1 )

FIELD OF THE INVENTION

The invention relates to a fuel injection method for an internalcombustion engine, especially of a motor vehicle.

BACKGROUND OF THE INVENTION

In internal combustion engines, a high compression ratio is sought forreducing the consumption and for increasing the torque. However, withincreasing compression ratio, the problem of an uncontrolled occurringself-ignition of the air/fuel mixture increases. A knocking combustionoccurs as a consequence. One distinguishes between two types ofknocking, the so-called acceleration knocking at low engine speed andhigh load (can be heard as a ringing) as well as the high engine speedknocking (which cannot be heard) at high engine speeds and high load.The high engine speed knocking is especially critical for the engine.

The knocking combustion generates pressure oscillations which superposeon the normal pressure course.

Continuous knocking causes severe damage to the engine (destroyedcylinder head seals, bearing damage, holes in the piston) and damage tothe spark plugs.

The knocking limit is dependent, inter alia, on the type of engine andon the fuel. The knocking resistance of fuels for fuel-injection enginesis characterized by the octane number (ON). The higher this number is,the more resistant to knocking is the fuel.

The oscillations emanating from the combustion chamber are detected bythe knock sensor. The output signal of the knock sensor is supplied to acontrol apparatus of the engine. The control apparatus evaluates theknock signal and initiates suitable countermeasures when a knockingcombustion is detected. For this purpose, the ignition time point is, asa rule, shifted so far in the direction “retard” until there is again adrop below the knock limit.

SUMMARY OF THE INVENTION

The present invention has as its object to improve a method of the abovetype so that an operation of an internal combustion engine is possibleat its operating limits without suffering a loss in torque because ofknocking combustion.

The method of the invention is for injecting fuel for an internalcombustion engine including an engine of a motor vehicle. The methodincludes the steps of: making a first injection in an induction stroke;determining a tendency-to-knock signal characterizing the danger of anoccurring knocking; and, making at least one second injection when thetendency-to-knock signal exceeds a threshold value.

The especially great advantage of the present invention is that anincrease of the maximum outputted torque of the engine is reached.Furthermore, the knocking limit is raised, that is, the engine becomesmore resistant to knocking.

A further advantage is that, with a knock control with the aid of doubleinjections, only a slight torque reduction results compared to the knockcontrol with the aid of a shift of the ignition angle in the directionof retard. A knock control via double injection and ignition angleintervention or a combined intervention of both is possible in order tooperate the engine at the optimal operating point.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawingswherein:

FIG. 1 shows schematically an illustration of an internal combustionengine having a control apparatus; and,

FIG. 2 shows an operating characteristic field of an internal combustionengine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As shown in FIG. 1, in an internal combustion engine having directinjection 10, fresh air is supplied to cylinder 38 or combustion chamber21 in cylinder 38 via an intake manifold 19 and an inlet valve 20. Thequantity of fresh air, which is supplied to the combustion chamber 21,can be controlled via a throttle flap 22. An air quantity sensor 23detects the fresh air flowing into the engine 10.

An injection valve 24 and a spark plug 45 are mounted in the cylinderhead 25. The fuel is brought to a working pressure by means of ahigh-pressure pump 26 and is injected into the combustion chamber 21 viaa fuel line 27 and injection valves 24. The injected fuel is ignitedwith the aid of the spark plug 45. A piston 44 is driven by theexpansion of the ignited fuel. Furthermore, the combustion chamber 21includes an outlet valve 28 for discharging the exhaust gases occurringin a combustion.

A knock sensor 37 and/or an ion flow sensor 37 are mounted on thecylinder 38. The oscillations which occur in the combustion are detectedwith the aid of the knock sensor 37. The ions occurring during acombustion are detected with the aid of the ion flow sensor 37. Thecombustion performance of the engine can be detected and especially aconclusion as to a knocking combustion can be drawn by evaluating thesignal of the knock sensor and/or of the ion flow sensor 37.

A lambda probe 29 is mounted in an exhaust-gas pipe 30. The oxygencomponent in the exhaust gas can be measured with the aid of the lambdaprobe 29 in the exhaust-gas pipe 30 whereby the air/fuel ratio can bedetermined in the mixture. A catalytic converter 46 is also mounted inthe exhaust-gas pipe 30. The catalytic converter 46 has the task ofconverting toxic exhaust-gas components such as CO, HC and NO into CO₂,H₂O and N₂.

An EGR line 31 connects the exhaust-gas pipe 30 to the intake manifold19. A portion of the exhaust gas is conducted from the output pipe 30into the intake manifold 19 because of the higher pressure in theexhaust-gas pipe 30. The exhaust-gas flow in the EGR line 31 can becontrolled with the aid of an EGR valve 32.

A tank-venting line 34 leads from a fuel tank or active charcoal filter33 to the intake manifold 19 whereby additional fuel can reach theintake manifold 19 and therefore also the combustion chamber 21. Thefuel flow in the tank-venting line 34 can be controlled by means of atank-venting valve 35.

The control of the entire engine 10 takes place by means of the controlapparatus 11. Further, the control apparatus 11 can control atransmission 16, a braking system 17 and/or any other additionalelectromechanical systems 18. The various sensors and actuators areconnected to the control apparatus 11 via signal and control lines 36.

The engine 10 can be operated in different operating modes which differessentially by the injection time point, the ignition time point, andthe cylinder charge. A switchover between the operating modes of theengine can be made with the aid of the control apparatus 11. Theessential operating modes of the engine are the homogeneous operationHOM and the stratified operation SCH.

In homogeneous operation, the fuel is injected into the combustionchamber 21 by the injection valve 24 during an induction phase caused bythe piston movement. At the same time, air is inducted via the throttleflap 22. The inducted air swirls the fuel which distributes in thechamber almost uniformly or homogeneously. The air/fuel mixture is thencompressed in order to be ignited by a spark plug 45. The ignitedair/fuel mixture expands and drives the piston 44. The occurring torqueis, in homogeneous operation, essentially dependent upon the position ofthe throttle flap 22 and is thereby essentially proportional to thefresh gas charge RL in the cylinders. The air/fuel mixture is adjustedas close as possible to lambda=1 or lambda<1 in order to obtain a hightorque and a low development of toxic substances with the combustion.The homogeneous operation is preferably adjusted in the full load rangeof the engine but can also be adjusted over the entire operating rangeof the engine.

In the stratified operation SCH, the throttle flap 22 is opened widewhereby the engine can be operated almost unthrottled. The fuel isinjected during the compression phase in such a manner that, at theignition time point, an ignitable air/fuel cloud is in the directvicinity of the spark plug. Then, the air/fuel cloud is ignited by thespark plug 45 and the piston 44 is driven by the following expansion ofthe ignited air/fuel cloud. The occurring torque is, in stratifiedoperation, dependent essentially on the injected fuel mass. Thestratified operation is adjusted in the part-load range of the engine.

In FIG. 2, the operating characteristic field of an engine having directinjection is shown.

In FIG. 2, M identifies the outputted torque and N identifies the rpm ofthe particular engine. A identifies the operating region in which thestratified operation is adjusted and B identifies the operating regionwherein the homogeneous operation of the engine is adjusted. Thecharacteristic line I identifies the operating limit of the engine whichis determined, inter alia, also by the knock limit of the engine 10.

In the control apparatus 11, the rpm N is continuously detected. Thetorque M is determined during homogeneous operation on the basis of thecylinder charge RL and, in stratified operation, on the basis of theinjected fuel mass RK. A tendency-to-knock signal is determined on thebasis of the detected cylinder charge RL and the rpm N or on the basisof the injected fuel mass RK and the rpm N. The tendency-to-knock signalis compared to a threshold value and double injections are initiatedwhen this threshold value is exceeded.

In this context, double injection means that the first injection takesplace in the induction stroke and the second injection takes place inthe compression stroke. The second injection causes the air/fuel mixturepresent in the combustion chamber 21 because of the first injection tobe cooled whereby the danger of an uncontrolled ignition of the air/fuelmixture is reduced.

Also, in knock endangered operating regions and before reaching theengine operating limits, the knocking limit of the engine 10 is reducedand/or the knocking behavior is improved by the double injections. Anincrease of the outputted maximum torque of up to 5% is obtainedespecially by carrying out targeted double injections in the region ofthe operating limits.

The proportion of the fuel mass to be injected in the first and in thesecond injection is determined in dependence upon the extent of thetendency-to-knock signal and/or from an engine parameter specificcharacteristic field stored in the control apparatus 11. The proportionof the first and second injections varies between 30 and 70% dependingon the operating state of the engine 10 and in dependence upon theextent of the tendency-to-knock signal. The first injection takes placetypically 300° ahead of TDC and the second injection takes placetypically 80° ahead of TDC.

In this embodiment of the fuel injection method of the invention, thetendency-to-knock signal for each individual cylinder of the engine 10is continuously detected and evaluated. In this way, it is possible tocarry out double injections in individual cylinders when detecting thedanger of knocking.

When detecting a “knocking” combustion, double injections are carriedout in addition to the knock control by shifting the ignition angle in adirection of retard. In this way, the ignition angle control depth ofthe knock control is reduced which leads to an improved control result,a reduction of consumption and an increase of the torque.

What is claimed is:
 1. A method of injecting fuel for an internalcombustion engine including an engine of a motor vehicle, the methodcomprising the steps of: making a first injection in an inductionstroke; determining a tendency-to-knock signal characterizing the dangerof an occurring knocking; and, making at least one second injection whenthe tendency-to-knock signal exceeds a threshold value.
 2. The method ofclaim 1, wherein the second injection takes place in a compressionstroke.
 3. The method of claim 1, comprising the further step of makingsaid at least one second injection when the engine is in the region ofthe maximum torque or in further knock-endangered regions at aninstantaneous torque with these regions being characterized in acharacteristic field.
 4. The method of claim 1, comprising the step ofincluding at least one of the output signals of a knock sensor and anion flow sensor in the tendency-to-knock signal.
 5. The method of claim1, comprising the further step of forming the tendency-to-knock signalstarting from operating characteristic variables of said engine.
 6. Themethod of claim 4 comprising the further step of forming thetendency-to-knock signal starting from at least one of the following:the cylinder charge, the injected fuel mass and the rpm.
 7. The methodof claim 1, comprising the further step of carrying out doubleinjections in addition to a knock control by shifting the ignition anglein the direction of retard when detecting a knocking combustion.
 8. Themethod of claim 1, comprising the further step of determining theproportion of the fuel quantity to be injected in the first and in theat least second injection in dependence upon at least one of thefollowing: the extent of the tendency-to-knock signal and a parameterspecific to the engine from a characteristic field.
 9. The method ofclaim 8, wherein the distribution factor of the injected fuel in thefirst and in the at least second injection amounts to 30 to 70%.
 10. Themethod of claim 1 wherein the first injection takes place 330° forwardof top dead center and the second injection takes place 80° forward oftop dead center.
 11. The method of claim 1, wherein said method isapplied in an internal combustion engine having direct injection. 12.The method of claim 1, wherein the at least second injection takes placespecific to the cylinder or specific to the cylinder bank.
 13. Anelectronic storage medium including a read-only-memory, for a controlapparatus of an internal combustion engine including an engine of amotor vehicle, on which a program is stored which can be run on acontrol apparatus including a microprocessor, and which is suitable forcarrying out a method comprising the steps of making a first injectionin an induction stroke; determining a tendency-to-knock signalcharacterizing the danger of an occurring knocking; and, making at leastone second injection when the tendency-to-knock signal exceeds athreshold value.
 14. An arrangement for carrying out the method ofinjecting fuel for an internal combustion engine including an engine ofa motor vehicle, the arrangement comprising: means for forming atendency-to-knock signal characterizing the danger of an occurringknocking; and, means for effecting at least a second injection when thetendency-to-knock signal exceeds a threshold value.